Aims. The characterisation of the stellar population in young high-mass star-forming regions allows fundamental cluster properties like distance and age to be constrained. These are essential when using high-mass clusters as probes for conducting Galactic studies. Methods. NGC 7538 is a star-forming region with an embedded stellar population unearthed only in the near-infrared (NIR). We present the first near-infrared spectro-photometric study of the candidate high-mass stellar content in NGC 7538. We obtained H and K spectra of 21 sources with both the multi-object and long-slit modes of LIRIS at the WHT, and complement these data with subarcsecond JHK s photometry of the region using the imaging mode of the same instrument. Results. We find a wide variety of objects within the studied stellar population of NGC 7538. Our results discriminate between a stellar population associated to the H ii region, but not contained within its extent, and several pockets of more recent star formation.We report the detection of CO bandhead emission toward several sources, as well as other features indicative of a young stellar nature. We infer a spectro-photometric distance of 2.7 ± 0.5 kpc, an age spread in the range 0.5−2.2 Myr and a total mass ∼1.7 × 10 3 M for the older population.

If the disappearance of the broad emission lines observed in changing-look quasars originates from the obscuration of the quasar core by dusty clouds moving in the torus, high linear optical polarization would be expected in those objects. We then measured the rest-frame UV-blue linear polarization of a sample of 13 changing-look quasars, 7 of them being in a type 1.9-2 state. For all quasars but one the polarization degree is lower than 1%. This suggests that the disappearance of the broad emission lines cannot be attributed to dust obscuration, and supports the scenario in which changes of look are caused by a change in the rate of accretion onto the supermassive black hole. Such low polarization degrees also indicate that these quasars are seen under inclinations close to the system axis. One type 1.9-2 quasar in our sample shows a high polarization degree of 6.8%. While this polarization could be ascribed to obscuration by a moving dusty cloud, we argue that this is unlikely given the very long time needed for a cloud from the torus to eclipse the broad emission line region of that object. We propose that the high polarization is due to the echo of a past bright phase seen in polar-scattered light. This interpretation raises the possibility that broad emission lines observed in the polarized light of some type 2 active galactic nuclei can be echoes of past type 1 phases and not evidence of hidden broad emission line regions.

More than 50 years after the dawn of X-ray astronomy, the dynamical parameters of the prototypical X-ray binary Sco X-1 are still unknown. We combine a Monte Carlo analysis, which includes all the previously known orbital parameters of the system, along with the Kcorrection to set dynamical constraints to the masses of the compact object (M 1 < 1.73 M ⊙ ) and the companion star (0.28 M ⊙ < M 2 < 0.70 M ⊙ ). For the case of a canonical neutron star mass of M 1 ∼ 1.4 M ⊙ , the orbital inclination is found to be lower than 40 • . We also present the best near-infrared spectrum of the source to date. There is no evidence of donor star features on it, but we are able to constrain the veiling factor as a function of the spectral type of the secondary star. The combination of both techniques restricts the spectral type of the donor to be later than K4 and luminosity class IV. It also constrains the contribution of the companion light to the infrared emission of Sco X-1 to be lower than 33%. This implies that the accretion related luminosity of the system in the K band is larger than ∼ 4 × 10 35 erg s −1 .